On Dec. 17, 1984, Southwest’s then-newest plane, the 737-300, took to the skies for its inaugural flight, retracing the Texas triangle of Dallas, Houston and San Antonio that formed the carrier’s first route network.

On Oct. 1, Southwest’s latest jet will fly that same route, two days after the carrier retires the last of its 737-300s, now affectionately referred to as the “Classics.”

In the 33 years between the launch of the Classic and the debut of Southwest’s Boeing 737 Max, the once-upstart carrier has transformed to become the country’s largest domestic airline, carrying more than 124 million paying passengers last year.

The Classic saw Southwest through the rapid growth of the company in the 1980s and 1990s, the financially troubled times after Sept. 11, 2001, and, over the last five years, the transformation of Southwest into an airline with international ambitions.

Now the next chapter of Southwest’s story will be written with the help of the Max, an update to Boeing’s time-tested 737 design.

On paper, the aircraft promises a host of technical improvements: better fuel efficiency, quieter engines and longer range. But for executives at Southwest and at other airlines, including American, who will soon receive their own 737 Max aircraft, the plane’s true potential to reshape route networks is only just being explored.

“It is a historic day for Southwest Airlines. [The Max] is maybe the final piece of our transformation journey,” chief operating officer Mike Van de Ven said of the Sunday launch of service. “It is an airplane that is going to be a big piece of our foundation moving forward ... it sets Southwest Airlines up for our next 20 to 30 years.”

Looks familiar

Looking at Southwest’s new 737 Max, it can be hard to distinguish it from its predecessor, the 737-800.

The Max has updated winglets and larger engines, but its dimensions are nearly the same. Inside, the Max has the same blue-clad interior and 175-seat layout found on the 737-800, although the galleys have been updated.

Southwest will have nine 737 Max aircraft in its famously all-Boeing fleet when they begin service on Oct. 1, and it plans to add 27 more by the end of next year. In 10 years, Southwest could have as many as 391 of the aircraft, a figure that represents more than half of the carrier’s current fleet size of about 700 aircraft.

A landing gear of a Southwest Airlines' new plane, the 737 Max, at headquarters in Dallas.

But perhaps most important is the 500 nautical miles of additional range Southwest says the jet will provide. Coupled with the lower operating costs, the Max can make existing routes more profitable and even make new destinations financially — and operationally — viable.

“The Max is a very exciting enabler in terms of what it will allow an airline to do ... it gives the airlines flexibility on where to fly and when” said Henry Harteveldt, a travel industry analyst and founder of Atmosphere Research Group.

The gallery in the back of Southwest Airlines' new plane, the 737 Max, at headquarters in Dallas, Tuesday, Sept. 12, 2017. (Jae S. Lee/The Dallas Morning News)

(Jae S. Lee/Staff Photographer)

Already, Norwegian Air Shuttle has been using the Max on trans-Atlantic flights from the northeast United States to western Europe, routes that are typically served by larger, wide body aircraft.

It’s a tactic that is already putting pressure on U.S. carriers, who have seen average fares across the Atlantic drop as much as 9 percent as low-cost carriers continue to expand in the market.

For Southwest, the Max will mean being able to fly farther to new destinations in South America, a tantalizing prospect as the carrier continues to expand its international network three years after it began flights to Mexico, Central America and the Caribbean.

It could also be the vehicle of choice if Southwest ever launches its long-anticipated service to Hawaii.

Inaugural flight

The first commercial flight aboard Southwest’s 737 Max will depart from Love Field at 7 a.m. Sunday. Among its passengers are expected to be a handful of aviation enthusiasts making the trip specifically to ride on the inaugural flight.

After completing its rendition of the "Texas triangle," the inaugural aircraft and its brethren will be flown on routes throughout Southwest's network, meaning it could be coming to an airport near you soon.